Attempts to control gene activity and/or increase the production of recombinant proteins in plants have been made using high level constitutive promoters, inducible promoters, tissue-specific promoters and developmental stage-specific promoters.
Systems for regulatable expression of genes have been reported in the literature and are generally based on modifying the activity of transcriptional regulatory proteins or by the use exogenous inducers (i.e., compounds) that specifically interact with a particular transcriptional regulatory protein. In either case, the result is to modify promoter activity by affecting the binding of transcriptional regulatory proteins to their DNA binding site and thereby controlling promoter activity for a given gene.
In addition, significant research efforts have been directed to constructing improved expression vectors, modifications of promoters and modifications of 5′ and 3′ untranslated sequences, with the goal of increasing the expression level of heterologous protein coding sequences. The regulated expression of transgenes in plants such that expression takes place in a manner that does not result in harm to the plant is the focus of extensive research.
Cereal seed storage proteins are a primary source of proteins in the diet of humans and agricultural animals worldwide. The bulk of cereal seed storage proteins are produced solely in the endosperm, a highly specialized tissue devoted to starch and protein biosynthesis and storage. Accordingly, cereal seed storage proteins are an attractive target for the regulated expression of transgenes and a need exists for effective strategies to enhance and regulate gene expression in seed tissues of cereal plants.